Influence of Vanadium on the Oxidation Resistance of the Intermetallic Phase Nb5Si3

The influence of vanadium additions on the oxidation resistance of the intermetallic phase Nb5Si3 was examined. Samples were produced by compacting mechanically alloyed powders using the field-assisted sintering technique. Oxidation experiments were performed under isothermal conditions at 800, 1000 and 1200 °C for oxidation times up to 100 h. Linear oxidation rate constants were found for all temperatures tested and the influence of the oxide scale morphology is discussed. At 800 °C very promising low weight gains were obtained and this particular oxide scale was examined thoroughly using scanning electron microscopy, electron dispersive spectroscopy and X-ray diffraction analysis to determine the oxide phases formed. As expected from the phase diagram the mixed oxide V2O5·9Nb2O5 was found as the major phase constituting the scale. No spallation of this mixed oxide was observed which is likely due to its lower volume gain as compared to pure Nb2O5. Together with the slower formation kinetics, Vanadium addition in the amount used seems to positively alter the oxidation behaviour of Nb5Si3.